The study delves into modeling the interface between Fiber-Reinforced Polymer (FRP) and concrete, with a specific emphasis on simulating the gradual deterioration of bond strength. A model rooted in continuum damage mechanics is integrated with an empirically derived relationship to address interfacial shear failure. Material models are defined for the concrete, the externally bonded FRP reinforcement, and the adhesive layer. These material models are implemented in finite element simulations, replicating experimental setups widely used to investigate the FRP-concrete interface. Key results are reported and discussed. More precisely, the numerically obtained load-slip relationships for the interface and visualizations of the damaged zones in concrete are provided. The numerical results are in close agreement with existing experimental data. The finite element analyses suggest that concrete degradation is not limited to the areas near the adhesive joint. This implies that the adhesive joint could influence the overall behavior of the structural elements, even when debonding failures are prevented by anchorage devices.

The use of fiber-reinforced polymer (FRP) composites for external bonding has become a popular and widely accepted technique for enhancing the strength of concrete structures due to its excellent mechanical performance, corrosion resistance, and ease of construction. However, premature debonding is a major challenge as it prevents the full capacity of FRP composites from being achieved, resulting in material waste. Recently, grooving the surface of concrete before bonding FRP has emerged as a potential solution to this problem. Several experimental studies have evaluated the bond strength of FRP-to-concrete joints with grooves. To facilitate the practical application of this technique, it is necessary to develop comprehensive reliability-based design guidelines that account for the uncertainty arising from various aspects such as materials, model errors, and loading. A critical factor of such analysis is the calibration of model uncertainty which significantly affects the accuracy of reliability-based design and analysis. The objective of this study was to measure the model uncertainty of the existing prediction model for FRP-to-concrete joint with a longitudinal groove by involving the model factor which is defined as the ratio of observed values from experimental test to calculated values from prediction models. To eliminate the potential correlation from critical parameters, the residual model factor was isolated from model factor by separating the systematic part. The lognormal distribution was found to be the most suitable distribution function to describe the residual model factor, and the mean and variance were determined. With this newfound knowledge, we are better equipped to account for uncertainties in the design and construction of FRP-to-concrete connections with grooves, which will ultimately result in more durable and reliable structural improvements.

Corrosion of reinforcement steel is a major issue for many structural concrete components, because it leads to strength reduction and may significantly reduce the service life. For this reason, fiber-reinforced polymer rebars (FRP rebars) have been developed, as they represent a viable alternative that may replace reinforcing steel for structures that are particularly susceptible to corrosion issues. However, structural design philosophies for these new materials are still in development and further research is needed to implement FRP rebars properly and safely in design codes but also to ensure that design calculations properly predict the actual behavior and performance of FRP reinforced structures.

This study was conducted to evaluate the strength and structural deformation behavior of flexural beams that were designed according to Eurocode 2 and, for comparison, according to different design methods pro-posed for FRP reinforced structures. With regard to the development of a uniform design concept for alternative reinforcement materials existing in Germany/Europe, different bending design concepts includ-ing the serviceability limit state were evaluated. In addition, the theoretically calculated and predicted strength/deformation were compared to the experimentally obtained measurements. A total of 15 flexu-ral beams, with ans overall length of 4.5 m (177 in.), a width of 200 mm (7.8 in.), and a height of 400 mm (15.8 in.), were cast; three of these beams (designed according to Eurocode 2) featured traditional steel rein-forcement, to serve as control group. The remaining 12 flexural beams were evenly allocated to capture the two alternative reinforcement materials, while generating three different reinforcement distribution patterns with comparable reinforcement ratios (equivalent cross-sectional areas). Thus, a total of six subgroups –three with GFRP and three with BFRP – each with two specimens, were analized. To test all beam in pure bending and to eliminate the influence from shear forces, two equally increasing loads were applied at the (longitudinal) third-points of the beams. Both deflections and loads were measured at several points to evaluate the structural performance of the FRP reinforced structural members.

The results showed that the deflection of the glass fiber reinforced bars at the design load capacity measured twice as much as the deflection of the control group. Almost three times as much deflection (at the same load) was observed for the concrete beams reinforced with basalt fiber rebars. In addition, it was observed that the concrete beams with glass and basalt fiber reinforcement bars showed a nearly elastic-elastic behavior up to the point of failure, whereas the steel-reinforced concrete beams showed an elastic-plastic behavior. However, the deformational behavior differed between the various beam types. While the prevailing equations properly captured the post-cracking performance of traditionally reinforced concrete beams, they do not adequately predict the deflections of FRP reinforced concrete beams. From the measurements and analyses, it was concluded that the serviceability limit state (SST) is more critical than the ultimate limit state (LTS) for the design of concrete flexural beams reinforced with FRP rebars.

The durability of the bond between carbon fiber reinforced polymer (CFRP) and concrete surface under freeze-thaw (FT) cycles is a very significant issue in the application of external CFRP strengthening of reinforced concrete structures. This paper presents an experimental and analytical study on the bond behavior between CFRP and concrete under FT cycles. In this study, the samples were exposed to freeze-thaw cycles in accordance with ASTM C666 where the temperature range varies between -18 °C to +4 °C. Moreover, the bond properties between CFRP and concrete were experimentally evaluated through single lap shear tests and compared with the analytical prediction models proposed in the literature. The failure modes of the control samples as well as the samples exposed to freeze-thaw cycles were presented in this research. In addition, the load-slip behavior was discussed. A non-linear bond-slip relationship between the CFRP-concrete interface was presented at 0, 100, 200, and 300 of freeze-thaw cycles. The results show that the cohesive failure of concrete substrate was observed for the control samples. On the other hand, the mode of the interface failure was changed after exposure to freeze-thaw cycles. In addition, the bond strength of the CFRP-concrete interface increases with increasing freeze-thaw cycles.

The current market of utility poles is growing rapidly. The dominant materials that are used for this purpose are generally wood, steel, concrete, and fiber-reinforced polymers (FRP). FRP poles are gaining wide acceptance for what they provide in terms of strength and durability, lack of maintenance and a high strength to weight ratio. Hybrid structures can combine the best properties of the materials used, where each part enhances the structure to provide a balanced structure. This study evaluates a hybrid structure composed of three main layers, an outer FRP shell, a hollow concrete core and an inner hollow steel tube, this whole system is to be utilized as a tapered utility pole. The outer FRP shell provides protection and enhances the strength of the pole, the concrete core provides stiffness, and the inner steel tube enhances the flexural performance while reducing the volume in consequence the weight of the structure compared to a fully filled pole. A new design for a 12-feet long hybrid FRP pole using finite element is presented in this paper. The design was based on a parametric study evaluating the effect of key-design parameters (i.e., the thickness of FRP, the volume and strength of the concrete, the thickness and diameter of the steel tube). Concrete strength affected the general performance of the pole, the decrease in concrete strength due to utilizing lightweight concrete was compensated with increasing the FRP pole thickness. For the same pole configuration, with incremental variation of the FRP thickness values from 3 mm to 7 mm up to the initial concrete cracking load, no significant variation of the pole top deflection was observed. However, at failure load the increase of FRP thickness from 3 mm to 7 mm decreased the ultimate tip deflection by 50%. New hybrid utility poles have the potential to be an interesting alternative solution to the conventional poles as they can provide better durability and mechanical performances.